The present invention relates generally to data storage devices. More particularly, the present invention relates to reducing power consumption in a hard disk drive system, particularly for applications with low-power portable devices.
Host devices such as computers, laptop computers, personal video recorders (PVRs), MP3 players, game consoles, servers, set-top boxes, digital cameras, and other electronic devices often need to store a large amount of data with fast read and write times. Storage devices such as hard disk drives (HDD) may be used to meet these storage requirements.
Referring now to FIG. 1, an exemplary hard disk drive (HDD) 100 is shown to include a hard disk drive (HDD) system on chip (SOC) 102 and a hard drive assembly (HDA) 104. The HDD 100 communicates with a host device 120. It is a design goal to provide as high a speed as possible for writing to and reading from the HDD 100. Maximizing reading and writing speed includes maximizing data transfer rates between the host device 120 and the HDD 100 and reducing the amount of time the host device 120 has to wait for a response from the HDD 100. Wait time or latency can occur while stored data is being retrieved or while the HDD 100 is being activated again from inactivity.
The HDA 104 conventionally includes one or more hard drive platters for storing data. A spindle motor rotates the hard drive platters. Generally the spindle motor rotates the hard drive platters at a fixed speed during read and write operations. One or more read/write actuator arms move relative to the hard drive platters to read and or write data to or from the hard drive platters.
A read/write device is located near an end of the read/write arm. The read/write device includes a write element such as an inductor that generates a magnetic field. The read/write device also includes a read element (such as a magneto-resistive (MR) element) that senses the magnetic field on the platters. A preamp circuit amplifies analog read/write signals.
When reading data, the preamp circuit amplifies low level signals from the read element and outputs the amplified signal to a read/write channel device. When writing data, a write current is generated which flows through the write element of the read/write device. The write current is switched to produce a magnetic field having a positive or negative polarity. The positive or negative polarity is stored by the hard drive platters and is used to represent data.
The HDD SOC 102 typically includes a buffer 106 that stores data that is associated with the control of HDD 100 and/or buffers data to allow data to be collected and transmitted as larger data blocks to improve efficiency. The buffer 106 may employ DRAM, SDRAM or other types of low latency memory. The HDD SOC 102 further includes a processor 108 that performs processing that is related to the operation of the HDD 100.
The HDD SOC 102 further includes a hard disk controller (HDC) 110 that communicates with a host device 120 via an input/output (I/O) interface 112. The HDC 110 also communicates with a spindle/voice coil motor (VCM) driver 114 and/or the read/write channel device 116. The I/O interface 112 can be a serial or parallel interface, such as an Integrated Drive Electronics (IDE), Advanced Technology Attachment (ATA), or serial ATA (SATA) interface. The spindle/VCM driver 114 controls the spindle motor which rotates the platters. The spindle/VCM driver 114 also generates control signals that position the read/write arm, for example using a voice coil actuator, a stepper motor or any other suitable actuator.
The I/O interface 112 of the HDD 100 communicates with an I/O interface 122 that is associated with the host device 120. The data communication may be in accordance with any suitable standard. In one example, the two I/O interfaces 112, 122 implement the Universal Serial (USB) Bus standard.
Particularly in applications in which the host device 120 is portable, low power operation is particularly desirable. The host device 120 includes a battery 124 that provides operating power to the host. In some cases, the battery 124 also provides operating power to the HDD 100, for example, over the USB connection between the two I/O interfaces 112, 122. The battery 124 may be recharged if depleted.
To extend the operating life of the battery 124, it is desirable to minimize or eliminate power consumption of components such as the HDD 100. Thus, when the HDD 100 is not required for reading or writing data, the HDD 100 may enter a low power mode in which active circuits are deactivated. However, when exiting the low power mode and becoming active again, the process of reactivating these circuits can produce a latency or wait time during which the host device 120 is waiting for a response. It would be desirable to provide a method and apparatus which produces the lowest power mode but which also returns to active state quickly for communication with the host device.